This invention relates to telephone systems and more particularly to non-dial or ring-down telephone connections to emergency operators through automatic electronic switching (EAX) equipment.
In the transition from the use of the mechanical step-by-step (relay) central office switching systems, known as Strowger switches, to EAX equipment in telephone communications systems, it is necessary that field telephones including freeway telephone instruments properly interface with the EAX. The freeway telephone typically is a non-dial instrument connected on dedicated lines to the central office switch which functions to connect it to an emergency operator such as police highway patrol dispatcher. The present method of providing telephone service via the step-by-step system is to cause the interface equipment to outpulse the number to be dialed (emergency operator) into the on-line step-by-step office which in turn translates these signals and reoutpulses the called number. This technique is slow and requires additional bulky equipment to connect the field instrument to the main relay switch which then completes the connection with the emergency operator.
In addition to the above, the relay switching equipment of the prior art monitors the originating call cable facility as well as the freeway telephone instrument for continuity when idle and for a permanent off-hook condition upon operator disconnect. It also activates central office common alarm if the conditions warrants. These features must also be accommodated in the interface circuit for the EAX.
This invention is directed to the provision of such an interface circuit.